Control system for ventilating apparatus



W. S. SCOTT.

CONTROL SYSTEM FOR VENTILATING APPARATUS. APPLICATION FILED MAY 23. 1919.

1,358,790. Patented Nov. 16,1920

WITNESSES: INVENTOR TTORNEY UNITED STATES PATENT OFFICE.

WIRT S. SCOTT, OF EDGEWOOD PARK, PENNSYLVANIA, ASSIGNOB T0 WESTINGHOUSE ELECTRIC 8t MANUFACTURING COMPANY, A CORPORATION. OF PENNSYLVANIA,

Specification of Letters Yatent.

Patented Nov. 16, 1920.

Application filed Kay 28, 1919. Serial No. 298,808.

To all whom it may concern:

Be it known that I, Wmr S. Soon", a citizen of the United States, and a resident of Ed ewood Park, in the county of Allegheny an State of Pennsylvania, have invented a new and useful Improvement in Control bystems for Ventilating A paratus, of which the following is a speci cation.

My invention relates to electricall heated ovens and particularly to systems 0 control for electrically heated enameling ovens.

The object of my invention is to control the supply of energy to the electrically operated heating coils of an oven of the above designated character by means of an electricallyoperated means for ventilating the oven.

An electrically heated enameling oven, of the intermittent type, as usually constructed comprises a suitable oven chamber provide with electric heating coils and with suitable doors for inserting and removing the work. Freshly japanned metal objects may be placed in the oven, the doors closed, and the heating coils then be energized to raise the temperature of the air and of the metal objects in the oven sutliciently to bake the enamel. As the'temperature of the metal objects is increased, oil and tar vapors are driven out of the enamel. As the vapors escape to the outside atmosphere through small ventilating pipes, some portions of them will condense on the inner surfaces of these pipes and harden. After lon continued use of the oven, 0. consi erable amount of material may thus be depos ted in the vent pipes, and, if continued lon enough, these pipes may'become clogge The deposited material ma also be 00 ed, because of the continued eating, and its ignition temperature may be lowered by reason of such coking.

If a quantity of freshly enameled metal objects is placed in such an oven while heated because of previous operation, the naphtha volatiles in the enamel may be driven out very rapidly as soon as the heating COIlS are again energized. An explosive m xture may thus be formed in the oven, and spontaneous combustion may take place in the vent pipes because of the coked deposits therein. The flame thus produced may be communicated to the exterior of the oven and cause an explosion of the mixture of air and volatile vapors.

In practising my invention, I provide an exhaust fan, driven by an electric motor, for ventilating the oven chamber, and place a minimum-current relay in the motor circuit. The circuit of the electrically operated heating coils is controlled by an electro-magnetic switch, and a circuit is so arran ed that the operation of the underload re ay will cause the electromagnetic switch to open and denergize the heating coils. As long as the vent pipe is not clogged and the motor load is normal, the relay will be in its normal position. If the vent pipe becomes so clogged as to reduce the quantity of air that can be removed by theexhaust fan, to an amount that may cause an explosive mixture, the motor current will also be reduced. The minimum-current rela in the motor circuit will then operate to s ort circuit the holding coil of the electro-magnetlc switch in the heater circuit, causing 1t %o open and thus deenergize the heater 001 s.

A thermostat is provided for rotection of the oven against overheating an operates to open the heater circuit in case of 9. dangerously high temperature. An on-and-oif push-button station is so arranged that the current through the heater coils may be in-- terrupted, if desired, independently of either of the above mentioned agencies.

The single figure of the drawing is a diagrammatic outline of the connections of the device embodying my invention, as applied to an electrically heated enameling oven.

. In the drawing, an inclosed oven chamher 1, having suitably arranged doors (not shown) for insertin and removing the work, is provided with a vent 2. A pipe 3 connects the vent 2 to an exhaust fan 4 that is driven by an electric motor 5,. In the drawing, the exhaust fan is shown as being direct-connected to the driving motor, but any suitable connecting means may be employed. A fused switch 6 connects the mo tor 5 .to a supply circuit 7, and a suitable controller (not shown) may be employed to start the motor. In one of the motor leads is placed a minimum-current relay 8, the o eration of which will be described later in detail.

A supply circuit 9 furnishes energy to heater coils 10 in the oven chamber, through an electromagnetic switch 11. A control circult is connected to the supply circuit 9 through a fused switch 12, an on-and-oif puslrbutton l3 and conductors 14, 15 and 15a, and comprises a double contact thermostat 16a located in the oven chamber and a circuit-closing relay 17. The relay 17 has a main bridging contact member 18 and an auxiliary bridging contact member 19. The

Y 2 1 that is connected to the' low contact terminal 25 of the thermostat and also connected to conductor 14. The high contact terminal 26 is connected to the conductors 15 and 15a. The contact terminals of the under-load relay 8 are connected, respectively, to the conductor 15a by means of a conductor 27, and to the conductor 22 by means of a conductor 28.

Assume that the circuits 9 and 7 are energized and 'that the switches 6 and 12 are open and the bimetallic strip 16 to be in contact with the low contact terminal 25, the operation oi the device and the system is as follows Close the switch 6 and bring the motor 5 up to normal speed by means of the controller. With a full opening of the vent pipe 3, the exhaust fan 1 will remove the normal amount of air. and the load on the motor 5 will be normal. The

current in the coil of the relay 8 will, theretore, be normal and will operate tcrlfold the armature in such position that the contact bridging member will not make operative connection between the contact terminals of the conductors 27 and 28. The switch 12 may now be closed and thepush button 13 operated to close the controlcircuit. This circuit will be as follows; from one side, of

, the supply circuit 9, through one meifiber oi the switch 12, through the push button 13,- conductor 14 to contact terminal 25, thtough the bimetallic strip 16 to the conductor 22. through the coil of the relay 17 to the conductor 15 the conductor 15, the second member of the switch 12 and to the other conductor of the supply circuit 9. his will o erate to close a circuit through the coil of the ele-tro-m'agnetic switch 11 as follows: from one conductor of the circuit 7, to the conductor2l), through the bridging contact member 18 to the conductor 26a} through the coil of the switch 11 and conductor 21 to the other conductor of thesupply circuit 7. The swith 11 will close and connect the circuit 9 to the heater was 10 in the oven chamber.

' The ma neto-mm member 19 of the relay 17 closes an auxiliary circuit from the conductor 22 to the fixed resistance 23, through the conductor 24, to the low contact 25 of the thermostat and also to conductor 14. If the temperature in the oven chamber rises so that the bimetallic strip 16 becomes disengaged from the contact terminal 25 but does not engage contact terminal 26, the following circuit will operate to keep the relay 17 in its closed position; from one conductor of the supply circuit 9 through one member of the switch 12, conductors 15 and 15a, the coil of the relay 17, the bridging contact member 19 to the resistance 2-3, conductors 24 and 14, push button 18, the other member of the switch 12 and to the other conductor of the circuit 9.

In case the vent 2 or the vent pipe 3 become clogged to such an extent as to allow the removal of relatively small amounts of air and volatile gases from the oven chamber 1,--a condition that might give rise to explosive mixtures in the oventhe current in the motor will be correspondingly decreased. This will allow the armature oi the relay 8 to drop and establish a short circuit across the terminals of the 'relay 17 as follows; through conductors 27 and 15a, the coil of relay l7, and conductors 22 and 28 to the other contact terminalof the relay 8. The armature of the relay 17 will drop and open the circuit through the coil of the magnetic switch 11. This switch will then open and interrupt the supply of energy to the resistors 10, andthe liberation of further quantities of volatile vapor from the enamel will, to a great extent, be prevented.- Thus,conditions in the exhaustsystem that might cause explosive mixtures in the oven chamber will operate to de'nergize the heating coils and thus render the operation of such ovens safer than heretofore.

If the temperature in the oven chamber 1 were to increase to such high valueas might result in damaged work, the bimetallic strip 16 of the thermostat 16a will engage the contact terminal 26 and will short circuit .the coil of the relay 17, the circuit being as follows; from one side of the supply circuit 9, through one member of switch 12, con ductor 15 to contact terminal 26, through bimetallic strip 16, conductor 22, Contact bridging member 19, through resistance 23, conductors 24 and 14 push button 13. the other member of switch 2 to the return conductor of circuit 9. This will cause the switch 11 to open, as described above in connection with the operation of the relay 8, and wil operate to'deenerg iie the heating coils.

The circuit of the relay may also be opened at any time by means of the push button 13, this action resulting in open ng the switch .11 and deenergiz'ing the heating c'oils 10. It is to be understand,- however.

that the push'button 13 and the thermostat- 16a are not essential. elements of my invention but are parts of a complete control sys tem in combination with the device embodyinglmy invention. it

arious modifications of the device may be made without departing from the spirit and scope of m invention, and I desire that only such limitations shall be imposed as.

are indicated by the prior art or are specifically set forth inthe appended claims.

,,I claim as m invention:

1, The combination with an oven structure comprising a chamber having an outlet for the removal of foreign substances, electric heating means for said oven, and means for controlling said electric heatin means, .of

Correction in Letters Patent No. 1,358,790-

means for positively removing oreign mat ter from said even, and means whereby the decrease of the flow caused by said removing means causes the operation of said controlling means to interrupt the operation of said heating means.

2. In an electric oven, the combination with an oven chamber having an outlet for the removal of foreign substances, means for electrically heating said oven, and means for controlling said electrical heating means, of means for removing foreign substances through said outlet, and means whereby the cessation of operation of the withdrawing means causes the controlling means to interrupt the operation of said heating means.

3. In an electric oven, the combination with an oven chamber having an air outlet,

means for electrically heating said oven, and means for controlling said electrical heating means, of means for drawing air and volatile vapor from said chamber through said outlet, and means for causing said control- 1920, upon the application of Wirt word "exterior read interior;

in the Patent Oifice.

[sun] with an oven chamber having an outlet for foreign matter, means for electrically heating said oven,'and means for controlling said electrical heating means, of an exhaust fan connected to said outlet, an electric motor for operating said fan, an underload relay in said motor circuit, said relay causing the operation of. said controlling means to interrupt the o ration of said heating means under Ere etermined conditions dependent upon t e amount of foreign matter withdrawn by said fan. s I a 5. In an electric oven, the combination with an oven chamber having an air outlet, means for electrically heating said even, and means fo'rcontrolling said electrical heating means, of means connected to said air outlet for causing a circulation of air through said oven chamber, and means for permitting the heating means to operate only when the air-circulating means is in operation.

6. In an electric oven, the combination with an oven chamber having an outlet for air and volatile vapor, means for electrically heating said oven, and means for controlling 7 0 said electrical heating means, of means for drawing air and volatile vapor through said outlet, and means for permitting the operation of the heating means only when a pre- WIRT s. soo'r'r.

It is hereby certified that in Letters Patent No. 1,358,790, granted November 16, S. Scott, of Edgewood Park, Pennsylvania, for

an improvement in Control Systems for Ventilating Apparatus, an error. appears in the printed specification requiring correction as follows: Page 1, line 53, for the and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case Signed and sealed this 1st day of February, A. D.,' 1921.

L. B. MANN,

Acting Uonwniseiomr of Patents. 

